/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.state;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;



import javax.annotation.Nullable;



/**

 * A {@link State} that can be read via {@link #read()}.

 *

 * <p>Use {@link #readLater()} for marking several states for prefetching. Runners can potentially

 * batch these into one read.

 *

 * @param <T> The type of value returned by {@link #read}.

 */

@Experimental(Kind.STATE)

public interface ReadableState<T> {

  /**

   * Read the current value, blocking until it is available.

   *

   * <p>If there will be many calls to {@link #read} for different state in short succession, you

   * should first call {@link #readLater} for all of them so the reads can potentially be batched

   * (depending on the underlying implementation}.

   *

   * <p>The returned object should be independent of the underlying state. Any direct modification

   * of the returned object should not modify state without going through the appropriate state

   * interface, and modification to the state should not be mirrored in the returned object.

   */

  @Nullable

  T read();



  /**

   * Indicate that the value will be read later.

   *

   * <p>This allows an implementation to start an asynchronous prefetch or to include this state in

   * the next batch of reads.

   *

   * @return this for convenient chaining

   */

  ReadableState<T> readLater();

}